Banting’s diet plays a pivotal role in the science of obesity—and, in fact, chronic disease—for two reasons. First, if the diet worked, if it actually helped people lose weight safely and keep it off, then that is worth knowing. More important, knowing whether “the sugary and starchy elements of food” are “really the chief cause of undue corpulence” is as vital to the public health as knowing, for example, that cigarettes cause lung cancer, or that HIV causes AIDS. If we choose to quit smoking to avoid the former, or to use condoms or abstinence to avoid the latter, that is our choice. The scientific obligation is first to establish the cause of the disease beyond reasonable doubt. It is easy to insist, as public-health authorities inevitably have, that calories count and obesity must be caused by overeating or sedentary behavior, but it tells us remarkably little about the underlying process of weight regulation and obesity. “To attribute obesity to ‘overeating,’” as the Harvard nutritionist Jean Mayer suggested back in 1968, “is as meaningful as to account for alcoholism by ascribing it to ‘overdrinking.’”

After the publication of Banting’s “Letter on Corpulence,” his diet spawned a century’s worth of variations. By the turn of the twentieth century, when the renowned physician Sir William Osler discussed the treatment of obesity in his textbook The Principles and Practice of Medicine, he listed Banting’s method and versions by the German clinicians Max Joseph Oertel and Wilhelm Ebstein. Oertel, director of a Munich sanitorium, prescribed a diet that featured lean beef, veal, or mutton, and eggs; overall, his regimen was more restrictive of fats than Banting’s and a little more lenient with vegetables and bread. When the 244-pound Prince Otto von Bismarck lost sixty pounds in under a year, it was with Oertel’s regimen. Ebstein, a professor of medicine at the University of Göttingen and author of the 1882 monograph Obesity and Its Treatment, insisted that fatty foods were crucial because they increased satiety and so decreased fat accumulation. Ebstein’s diet allowed no sugar, no sweets, no potatoes, limited bread, and a few green vegetables, but “of meat every kind may be eaten, and fat meat especially.” As for Osler himself, he advised obese women to “avoid taking too much food, and particularly to reduce the starches and sugars.”

The two constants over the years were the ideas that starches and sugars—i.e., carbohydrates—must be minimized to reduce weight, and that meat, fish, or fowl would constitute the bulk of the diet. When seven prominent British clinicians, led by Raymond Greene (brother of the novelist Graham Greene), published a textbook entitled The Practice of Endocrinology*2 in 1951, their prescribed diet for obesity was almost identical to that recommended by Banting, and that which would be prescribed by such iconoclasts as Herman Taller and Robert Atkins in the United States ten and twenty years later.

Foods to be avoided:

1. Bread, and everything else made with flour…